1. Field of the Invention
The present invention relates to an antenna, and more particularly, to a dual frequency broadband antenna.
2. Description of the Related Art
With the developments in wireless communications technology, many electronic devices, such as notebooks and mobile phones, now incorporate wireless communications abilities. In order to receive and transmit signals, these electronic devices need to have an antenna for detecting electromagnetic radiation.
Since both mobile phones and notebooks have became important in the daily lives of many people, if it were possible to combine these two devices, such a combined-function device would offer significantly more convenience for users. However, the prior art antennas for typical mobile phones usually have a narrow frequency bandwidth of about 70 MHz at a low frequency range (900 MHz), and a narrow frequency bandwidth of about 120 MHz at a high frequency range (1800 MHz) when a VSWR (Voltage Standing Wave Ratio) is less than 4. Additionally, the antenna efficiency of the typical mobile phones is typically low as around 20˜30%; therefore, if the prior art mobile phone antenna is installed in a notebook, the antenna will not provide very satisfactory results.
A prior art technology has disclosed a dual frequency antenna that can provide a wider frequency bandwidth than earlier mobile phone antennas. Please refer to FIG. 1. FIG. 1 shows a prior art antenna 90, as disclosed in U.S. Pat. No. 6,861,986. As shown in FIG. 1, the antenna 90 has a radiating element 91, a connecting element 92 and a grounding element 93. The connecting element 92 has a first end 921 and a second end 922, wherein the first end 921 is coupled to the radiating element 91, and the second end 922 is coupled to the grounding element 93. The antenna 90 can be used for WWAN, WLAN 802.11a or 802.11b, Bluetooth or GSM communications systems. Compared to the typical mobile phone antenna, the antenna 90 has a wider frequency bandwidth, usually having a frequency bandwidth of about 120 MHz at the low frequency range (900 MHz) and a frequency bandwidth of about 480 MHz at the high frequency range (1800 MHz) when the VSWR is less than 3.
Although the prior art technology already provides a broadband antenna, the frequency bandwidth still can be improved. Furthermore, if a new antenna can provide a wider frequency bandwidth with a smaller size, such a new antenna would have better platform compatibility characteristics, and would have lower manufacturing costs.
Therefore, it is desirable to provide a dual frequencies broadband antenna to mitigate and/or obviate the aforementioned problems.